This invention relates to telecommunications network and more particularly to a messaging method therefor by which the origin and destination nodes of a failed path can receive information on which spans or links remain usable in the failed path.
A telecommunications network comprises a plurality of nodes connected together by spans and links. These spans and links are for the most part fiber optical cables. A path is defined in the network as the connection between the two end nodes by which information or traffic can traverse. One of these end nodes is defined as an origin node while the other is the destination node. There could be a number of paths that connect the origin node to the destination node. And if one of those paths that carries the traffic is disrupted, another path can be used as an alternate for rerouting the traffic. Thus, for such path based approach for restoring disrupted traffic in a telecommunications network that is provisioned with a distributed restoration algorithm (DRA), the origin and destination nodes are taken into consideration.
In a telecommunications network, it is likely that when a fault occurs, only a single link or span along a path is affected. Such catastrophic event may be due to, for example, a cable cut. The remainder of the path through the network on either side of the failure may therefore remain intact and could be used for circumventing the failed portion. Yet a path-based DRA provisioned network nonetheless may disregard the, intact portions and seek a completely different alternate route for restoring the traffic. This can be a problem because indiscriminate selection of a candidate path to restore one failed path can preclude the restoration of other simultaneously, or subsequently failed paths, as damage to a single span in a network can cause the failure of many paths that may happen to pass through the same span. Therefore, a DRA provisioned network must take into account all such end-to-end paths that need to be restored in order to ensure the highest possible degree of restoration following a failure.
There is therefore a need for an improved DRA provisioned path-based restoration scheme that allows the intact portions of a failed path to be ascertained and made available for forming alternate restoration paths, to thereby improve the efficiency and the completeness of the restoration.
To enable the DRA provisioned network to utilize the intact portions of a failed path, the present invention messaging technique provides information to both the origin and destination nodes of a failed path on which spans or links remain intact leading up to the point of failure.
To achieve this end, the failure is first detected by the adjacent custodial nodes bracketing the fault. Each of these custodial nodes adjacent to the failure then would initiate the propagation of a xe2x80x9creusexe2x80x9d message to either the origin node or the destination node. This reuse message has a variable length route information field and an identifier identifying it as a reuse message. As the reuse message is propagated from node to node back to the origin or destination node, each node through which the reuse message passes would append its own unique node identification (ID) to the route information field. Thus, when an origin or destination node receives the reuse message, it can read from the route information field of the reuse message a description of the intact portion of the path.
By allowing the restoration logic to take into account the intact portions of the original paths, better restoration decisions making use of the intact portions of the path can take place. In a preferred embodiment, such restoration logic is only permitted to apply the intact portions to the restoration of the failed path that originally included the portions. In other words, such intact portions are restricted for use in restoring the failed path. Such restriction considerably simplifies the restoration process and avoids the possibility of unforeseen problems.
It is therefore an objective of the present invention to provide a method of communicating the description of the intact portions of a failed path to the origin and destination nodes of a failed path.
It is yet another objective of the present invention to provide a method of determining the portions of a failed path that remain usable for carrying traffic.
It is moreover an objective of the present invention to provide a method for identifying the reusable links or spans that connect nodes of a failed path so that these links or spans can be used by an alternate path for restoring the disrupted traffic.